This invention relates in general to trackballs and in particular to a simplified trackball arrangement that requires a single emitter-detector combination for each chopper wheel as compared to the emitter and two detectors for the prior art chopper wheels.
Trackball arrangements are well known in the art for conveying information regarding the distance and direction of movement of a ball over a surface. These arrangements are commonly used in computer "mouses" and for other similar type operations where x-y movements are to be determined. Conventional trackball mechanisms include a trackball that is drivingly engageable with a pair of rollers, each of which, in turn, drives a respective chopper wheel. The chopper wheel comprises a disk that has a plurality of evenly spaced slots about its periphery. The slotted chopper wheel interrupts an infrared (IR) beam that is formed by an IR emitter and detected by an IR detector that are positioned on opposite sides of the chopper wheel. The distance travelled by the trackball is determined by the number of slots passing between the emitter-detector combination. A second detector that responds to the same IR beam from the emitter of the emitter-detector combination is used to determine the direction of movement of the chopper wheel. The outputs from the IR detectors (for both the X and the Y chopper wheels) are integrated to provide a resultant directional movement indication for use by the computer or other output device.
With the invention, one of the IR detectors for each chopper wheel is eliminated thus simplifying the trackball structure and lowering its cost.